The present invention relates to a device for heating plastic (PVC) tubing or pipe for the purpose of bending, shaping or forming heat-softened plastic tubing into turns, bends, and/or curved shapes.
Rigid plastic tubing, such as polyvinylchloride (PVC) tubing, is widely used in construction industries to form electrical conduits, plumbing, ducting, interior support structures, etc. The PVC tubing is typically supplied as stock material in predetermined lengths at a construction site, and commonly must be bent, shaped, or formed with turns, bends or curves to specific job layout requirements.
Various methods have been used for heating PVC tubing at a job site. Heating PVC tubing over an open flame is wasteful, can result in uneven heating, and can be dangerous. The torch method can result in burning the heated PVC pipe and is dangerous to use near combustable materials. It also creates toxic fumes while the PVC pipe is heated or burned. It also requires gas to be provided from propane cylinders that need to be refilled regularly, costing the contractor time and money.
Box heating ovens with resistance-type heating elements have been used, but are expensive, of fixed dimensions not readily adaptable to bending tubing of different lengths, and are energy inefficient and expensive. Use of box heating ovens is also very labor intensive and must be constantly monitored during the heating procedure. Examples of box heating ovens are shown in U.S. Pat. Nos. 6,971,872, 6,561,797, 5,017,760, 3,843,858, and 1,407,412, and Canadian Patent 1,007,023 issued March 1977.
U.S. Pat. No. 6,033,213 shows a tubular heating device in which hot air from an air heat gun or blower is injected into a port in the midsection of a tubular housing against a diffuser plate and directed along the PVC pipe length on both sides. However, this method can result in excessive heat at the diffuser plate and uneven heating of the outside surface of the pipe compared to its inside surface.
Other PVC pipe heating methods use flexible heater elements that are inserted into the PVC pipe itself to heat it from the inside. (PVC BEND IT) This method is very labor intensive, expensive, and only heats the pipe from the inside surface. Also, a different heating element would be needed to heat different pipe lengths and diameters.